Blowing or Casing Glass Colour Properties
These colours are constructed around 8 different base glasses, but the majority fit into three broad families.
We use a 28% lead oxide crystal matrix for all but the reds and yellows and photosensitive glass.
This base is easy to remelt, not prone to devitrification and gives particularly dense and brilliant colouration. Lead glasses are about 15% more elastic than common soda lime glasses, allowing for a greater expansion mismatch.
The reds and yellows, #’s 70-77 series, are lead free, containing either CdS.xSe or Cu2O. Based on a Soda Zinc matrix, they are colloidal colours and work best with soda lime clears with a close expansion match around 96 x 10-7 coefficient. See Gaffer Batch Not as elastic as the lead based colours. To avoid over striking, and consequently inducing opacity, try to work cold, with as few reheats as practicable.
With the exception of #100 Enamel White and the Gold colours #’s 110 – 114, all of the colours are generated from the same lead free base. This makes our opal range unique, allowing colours to be combined with identical viscosity characteristics. The colours are dense, with overlays easily able to block out each other. This range has a relatively high softening point. We recommend a soak temperature of around 600oC (1110oF) before transferring rod to be heated in the glory hole, otherwise internal cracking (which you may not hear) will create small bubbles.
Chip and Powder:
Powder comes in two forms: Talc and Grain powder
Chip sizes are as follows:
KO 0.25 – 0.5mm, K1 0.5 – 2.0mm, K2 2.0 - 4.0mm K3 4.0 – 8.0mm.
Sizing is approximate, representing 95% of a sampling.
#’s 070, 071, & 072 are not offered in either talc or grain powder.
Rods: The rods vary in diameter between 30-32mm (11/4in).
The length is up to 400mm (16 in)
Glass blowers think weight rather than volume when they buy glass. Note from the photograph how all three rods are of equal length and diameter but weigh different amounts. Soda zinc and opal glasses are approximately 2.5g/cc, 28% lead glasses are approx. 3.0g/cc and Enamel White #100 is 3.7g/cc. Contrary to our competitors, most of our opal colours yield 20% more volume per weight owing to the fact they are lead free.